Submarine.

Submarine. I INTRODUCTION Submarine, type of warship designed to operate completely underwater for long periods of time. They are designed to submerge and surface, and to maneuver quietly underwater to avoid detection. Submarines can launch a variety of weapons including torpedoes, mines, antiship and land-attack cruise missiles, and submarine launched ballistic missiles (SLBMs) with nuclear warheads. Modern submarines have a cylindrical hull that tapers at one end and forms a blunt, rounded nose at the other end. They are usually made of high-quality steel but may also be made out of titanium. Most modern submarines are powered by nuclear energy, though some rely on diesel engines and electric batteries for propulsion. Submarine design and complexity have evolved considerably since the first efforts to build submarines over 500 years ago. Accounts of pre-industrial submarines of the 1500s describe small oar-propelled wooden boats covered in treated leather, which would allow them to travel at or just below the water's surface for short distances. In contrast, the nuclear attack submarine USS Seawolf is 107.6 m (353 ft) long, made of steel, and is armed with a variety of weapons. The USS Seawolf has a crew of 130, and can travel around the world completely submerged at depths in excess of 460 m (1500 ft). The use of submarines in warfare has evolved steadily with improvements in their diving ability, underwater endurance, and weapons technology. Submarines of the 1700s and early 1800s were larger in size than their predecessors, but were still primitive hand-powered ships, with rudimentary and often ineffective explosive weapons. Periscopes, which enabled submariners to view the surface waters while remaining shallowly submerged, were added to submarines in the mid-1800s. By the outbreak of World War I (1914-1918), most industrialized countries had acquired a first generation fleet of crude but effective diesel-electric submarines. World War II (1939-1945) submarines improved upon these designs with better engines and longer ranges. Nuclear power, first introduced into a submarine in 1954, extended the range of a submarine even more. Nuclear-powered submarines can stay submerged for longer periods than diesel subs, since nuclear engines don't need to surface for oxygen. Submarines are valued for their ability to roam undetected in the ocean, and many navies operate submarine fleets. In the 1950s, when international tensions between the United States and the Union of Soviet Socialist Republics (USSR) were at their peak, there was a maximum of about 650 submarines of all types among the major powers. Since the collapse of the USSR in 1991, the number of advanced submarines in the world has shrunk considerably. In the late 1990s, five countries--the United States, Russia, the United Kingdom, France, and China--continued to operate a total of about 150 advanced submarines, most of them nuclear-powered. Several other countries continue to operate older, less sophisticated submarines. II TYPES OF SUBMARINES Two basic types of submarine are built and used by the navies of today: attack submarines and ballistic missile submarines. All modern submarines operate in similar ways, but these two types differ in size, construction, and purpose. A Attack Submarines The attack submarine is a fast submarine that is primarily designed to hunt other submarines or surface warships. Attack submarines are powered either by a dieselelectric propulsion system or a nuclear reactor. An American Los Angeles class attack submarine is 109.7 m (360 ft) long, with a crew of 141. Apart from attacking other ships, they can also strike land targets with cruise missiles; conduct secret scouting missions; land small teams of commandos; and lay mines (see Mine, warfare). The attack submarine is designed for stealth and speed, and normally operates on its own rather than as part of a fleet. Since the enemy can detect direct communications, an attack submarine usually limits the number of direct transmissions it broadcasts. Like most submarines, it receives orders by way of encoded communications from satellites. B Ballistic Missile Submarines Ballistic missile submarines are specially designed to carry and launch intercontinental nuclear-tipped missiles from vertical launching tubes. An American Ohio class ballistic missile submarine is 170.7 m (560 ft) long--much longer than an attack sub--and carries a crew of 163. These submarines form part of a country's strategic nuclear force. Military strategists use the threat of a retaliatory submarine-launched missile attack to deter an enemy from starting a nuclear war. The strategy is simple: Even if the aggressor were able to destroy all of its enemy's land-based missiles in a first-strike, the enemy's ballistic missile submarines could deliver a devastating counter-blow, thus assuring what defense planners have called mutual assured destruction. Because of their mission to deter attack on their respective countries, ballistic missile submarines are designed to operate with extreme quiet in deep ocean patrol and evade detection during their patrols, which last from a few weeks to as many as 70 days at sea. Since an enemy cannot detect these subs, they pose a constant threat to a potential aggressor. The U.S. Navy also operates several smaller submarine-type underwater vessels. These are much smaller than submarines, and are used for military research, underwater rescue, and salvage operations. For information on these and other underwater vehicles, see Submersible Craft. III HOW A SUBMARINE WORKS Submarines rank among the most complicated warships ever put to sea, and are carefully designed to maximize performance and ensure safety. Submarines must be able to surface and dive quickly, maneuver safely underwater for months at a time, receive and transmit communications, operate quietly to avoid detection, and provide a habitable space for the crew. Regardless of the type of submarine, they accomplish these tasks in similar fashion. A Design The design and development of a submarine involves a complex series of compromises between the hull size and shape, the power plant system, weapons and sensors, and the desired performance in speed, depth, and silencing. The primary limitation is that of submerged displacement: The total weight of the entire submarine must weigh less than the volume of water it displaces in order for it to float. Streamlining is another important factor in submarine design. Early submarines, which could stay submerged only for a short time, operated mainly on the surface and often had large deck guns for shelling ships and surface targets. Likewise, they had bulky structures, called the sail or bridge, that rose above the middle section of the submarine. Underwater performance and endurance gradually increased as technology improved, and the deck guns, which hampered underwater speed, eventually faded from use. Beginning in the 1950s, submarine builders embraced the albacore-shaped hull--a smooth, stiffened cylinder with a spherical bow and tapered stern--as the most efficient underwater design. This shape allows the submarine to operate at relatively great depths, and to maneuver and accelerate with minimum drag through the water, while providing space to house the necessary mass of internal components. B Propulsion Modern submarines use either diesel-electric or nuclear power to drive the sub's propeller and to provide internal electric power. Diesel-electric power emerged as the most efficient propulsion system for submarines in the early 20th century, following unsuccessful attempts to use steam or gasoline power. While on the surface, the submarine uses a diesel engine to drive the propeller and generate electricity. When submerged, a battery-driven electrical motor takes over for propulsion and power. The diesel engine recharges the batteries. Using the diesel engine requires air, however, and so a submarine has to surface and thus expose itself to attack. German engineers solved this problem in the design of their World War II submarines, called U-boats. They did so by developing the snorkel, a retractable tube that can be extended above the surface of the water while the submarine operates at periscope depth--about 18 m (60 ft) below the surface. The snorkel provided the air to burn fuel in the diesel engine and vented off the exhaust fumes produced by the engine. Using the snorkel gave a margin of safety for submarines as they recharged their batteries, and allowed submarines to extend their underwater range considerably. The successful design in the early 1950s of a nuclear reactor small enough to fit inside a submarine hull was the most significant advance in submarine technology since the advent of diesel-electric propulsion a half-century earlier. A U.S. Navy team led by then-Captain Hyman G. Rickover engineered the breakthrough. Their success followed years of scientific speculation that a controlled nuclear fission reaction might be harnessed to power submarines. The theory is as simple as the reactor designs are complex: A controlled nuclear reaction, which takes place within a pressure vessel, produces enormous heat energy. This heat is channeled through a piping system that, in turn, heats water in a second, separate circuit of pipes. The heated water turns to steam, which passes through a turbine to power the submarine's propulsion drive. The steam also provides internal electric power via a turbine-driven generator. Because the nuclear reactor does not need access to fresh air, a modern nuclear submarine can cruise submerged for an unlimited amount of time. During long stretches underwater, the vessel replenishes its supply of breathing oxygen through hydrolysis, a chemical process that extracts oxygen from seawater. C Surfacing and Diving Submarines use a system of tanks that can be filled with and emptied of seawater to control the buoyancy of the warship. These tanks, called ballast tanks, permit diving and surfacing. The modern submarine has an array of wrap-around ballast tanks surrounding the inner (or pressure) hull of the submarine, where the crew lives. The ballast tanks are filled with seawater to reduce buoyancy for the dive. To surface, compressed air is ejected into the tanks, forcing out the ballast water and increasing the ship's buoyancy. By varying the number of tanks that are filled with water, a submarine can run at different underwater depths. Maneuvering underwater is accomplished by adjusting the ship's rudder and control planes. These are short, hydraulically powered wing-shaped surfaces. The rudder is located at the rear of the sub near the propeller, and controls left and right movement. Two sets of control planes are mounted near the rudder and at the forward end of the sub, either on the hull or bridge structure. The control planes control upward and downward movement through water, and help the submarine surface and dive. World War II-era and later submarines have a separate set of controls for the stern (rear) planes and fairwater (forward) planes, but one person can also operate the submarine at a single station. By flooding the ballast tanks with water and controlling the planes, the submarine can dive through the water to the desired depth. Three factors govern how a modern submarine functions in underwater combat: its operating depth, sound silencing ability, and navigational capabilities. A submarine's operating depth is limited by the toughness of the pressure hull and penetrations for seawater intake pipes, torpedo tubes, and other openings. World War II-era submarines could only venture safely to a depth of about 120 m (about 400 ft), while modern nuclear submarines are believed to be able to descend safely to depths in excess of 460 m (1500 ft)--the precise figures are highly classified. D Silent Running The primary means of locating an enemy submarine is through sonar (SOund Navigation And Ranging). A sonar system detects sounds produced by the sub's engines and by its passage through the water, or it detects the echo of sonar signals bounced off a target. Submarines operating underwater avoid detection by silencing the sounds they make. The basic hull and propulsion systems of a modern submarine are specially designed to minimize noise. Some submarines have special rubberized coatings or tiles affixed to the exterior hull to absorb enemy sonar signals. Other subs mount their machinery or other noise-making equipment on flexible rubberized baffles to prevent the sound vibrations from being transmitted through the hull. Another technique for avoiding detection is to hide the submarine in pockets of colder seawater, which form an acoustic layer that sonar waves can not penetrate. E Navigation and Communication Modern submariners have much better navigational tools than their earlier counterparts. During World War II, submarines, as well as other ships and aircraft, began using radio signals beamed from ground stations to calculate their approximate location. (To learn how such radio navigation works, see Loran). Until the 1960s, however, submarine navigators still used handheld sextants to plot their positions by the stars. Missile submarines in the 1960s and 1970s began using mechanical dead reckoning calculators and charts of the known landscape features on the ocean floor to chart their locations. Dead reckoning calculators use a previous position, the submarine's speed and direction, and the time traveled to calculate position. Because they did not take currents or variations in speed into account, these were also relatively inaccurate. Powerful digital computers and sophisticated gyrocompasses (gyroscopes used as compasses for direction-finding) now help submarines navigate. Submarines also use the Global Positioning System satellite network, which provides navigational accuracy measured in meters as opposed to kilometers. See also Navigation. Submarine communications remain limited today more by tactical necessity and the need for stealth than by limits in modern communications capabilities. Submarines have retractable antennas for receiving and transmitting radio messages, although on most missions the submarines operate on electronic silence, merely copying incoming messages broadcast by satellites. Also, both missile and attack submarines in the U.S. Navy can receive messages via very low frequency radio waves, which can be picked up by a trailing wire antenna while they operate submerged. F Life on a Submarine The quality of life for submariners at sea has improved along with technological improvements such as larger hulls, cleaner propulsion systems, and increased internal electricity and water. Submarines of the 1920-1945 era were cramped and poorly-ventilated, subjecting sailors to occasional belches of diesel exhaust. Sailors rarely changed clothes and showered only occasionally due to the scarcity of water. They shared bunks with other sailors due to space shortages, and lived on canned food due to limited galley facilities. While the inside of a submarine remains a cramped, equipment-studded cylinder, modern sub crews enjoy air conditioning, a variety of meals (thanks to refrigerators and freeze-dried foods), and recreational diversions, such as personal computers, videotape machines, and even compact exercise equipment. Larger missile submarines have even more features: The Trident missile submarines have an unofficial jogging track on one deck on the outside of the array of missile tubes, and the Russian Typhoon submarine features a miniature greenhouse with flowers and a small swimming pool for its crewmen. Nevertheless, all navies carefully screen recruits for their submarine services to ensure that the sailors can withstand the psychological and physical pressures of inhabiting a closed environment for months at a time. IV HISTORY OF SUBMARINE DEVELOPMENT Efforts to build submersible boats began in Europe over 500 years ago. Although the technology was not sophisticated enough to create a successful submersible craft, several attempts were made with varying degrees of success. The English scientist William Bourne in 1578 wrote of the possible use of ballast tanks to enable a submersible craft to descend and rise to the surface, though he never built one himself. In 1620 Cornelis Drebbel, a Dutch inventor, created several prototype submersibles resembling two wooden rowboats, one atop the other and bound with leather for a watertight skin. These were propelled by oars that emerged from the hull through resilient, watertight openings. According to contemporary accounts, Drebbel tested his crafts several times below the Thames River in London, England. Historians consider Drebbel's tests the first practical use of a maneuverable submarine. A The First Submarines For the next two centuries, scientists and inventors in America, England, France, Germany, and Italy attempted to create a true submersible warship with little success. An American submarine was used in an attempt to sink an enemy ship during the Revolutionary War (1775-1783). Submarines continued to be improved, and were again used during the American Civil War (1861-1865). The Turtle was designed by Connecticut inventor David Bushnell for use against the British fleet blockading New York in 1776. The Turtle was an egg-shaped craft, slightly larger than an adult man, constructed of wood and designed to briefly submerge under an anchored enemy ship. Its one-man crew could propel the craft by vigorously cranking a hand-turned propeller. The boat's weapon was an explosive charge that could be screwed into the underside of the target ship's hull. Continental Army Sgt. Ezra Lee made the one and only attempt to use Bushnell's craft in action, floating the Turtle against the hull of the British HMS Eagle in 1776. The operation was foiled when Lee could not affix the explosive device to the Eagle, whose hull was copper-plated. The Turtle and its crew of one escaped. In 1800 the American inventor Robert Fulton built a 6.4-m (21-ft) submarine named the Nautilus, which was similar in shape to the modern submarine. Fulton introduced two important innovations: rudders for vertical and horizontal control and compressed air as an underwater supply of oxygen. When submerged, the Nautilus was powered by a hand-operated, four-blade propeller. On the surface the boat was propelled by means of sails attached to a folding mast. The Confederate submarine H.L. Hunley was built in 1862 to aid the South in breaking the Union Navy's blockade of its ports during the Civil War. The Hunley went into action against the Union steam sloop USS Housatonic, which was anchored off Charleston, South Carolina. The Hunley carried an explosive charge attached to a long pole, or spar, affixed to the front of the craft. The mission was successful but the explosion inadvertently sank the Hunley as well. During the latter half of the 19th century, many attempts were made to develop an adequate means of submarine propulsion. Inventors experimented with compressed air, steam, and electricity as power sources. American inventor John Philip Holland, who used a dual-propulsion system, developed the first practical submarine with an efficient source of power. Launched in 1898, his submarine was equipped with a gasoline engine for surface cruising and an electric motor for underwater power. In 1900 the U.S. government purchased the boat, which had an overall length of 16.2 m (53 ft), and named it the USS Holland. B The World Wars At the outbreak of World War I in 1914, submarine technology had evolved to the point that the United States, the United Kingdom, Germany and Russia had all developed diesel-powered submarines that could operate on electrical batteries underwater. The U.S. Navy built 28 subs between 1901 and 1914, increasing its small fleet to 50. World War I introduced the concept of unrestricted submarine warfare, in which not only enemy warships but merchant vessels of all nations found in enemy waters were subject to unannounced attack. The German U-boat service, with an average of only 30 submarines at sea at any one time, put a stranglehold on shipping and merchant supply lines, and nearly brought the United Kingdom to its knees in four years of conflict. Two decades after the end of World War I, submarines again became important weapons as the world entered World War II. Between the wars, scientists and shipbuilders had improved the basic technology of the diesel-electric submarine. They also had made advances in torpedo design as well as in ways to identify, locate, and destroy enemy subs. When the United States entered the war against Germany and Japan after the December 7, 1941 attack on Pearl Harbor, the U.S. Navy found itself with only one effective weapon in the Pacific theater--its submarine force. On the other side of the North American continent, Germany found the only weapon it possessed that could inflict damage on America was its battle-scarred U-boat force. Both navies went to war with limited numbers of subs. The Germans had only 6 operational U-boats out of 51 within reach of the North Atlantic coast at the outbreak of war, while the U.S. Navy at Pearl Harbor had only 14 effective submarines in December 1941. Both sides were also plagued by flawed torpedoes that frequently failed to explode. Nevertheless, both navies scored an immediate impact with submarines. A handful of German U-boats soon wreaked havoc in coastal shipping lanes from Halifax, Nova Scotia, to the Caribbean Sea, while U.S. submarines began long trans-Pacific deployments into Japanese-controlled waters to target both merchant shipping and naval forces. The Allies would go on to win the Battle of the Atlantic against the U-boats in May 1943 through superior antisubmarine warfare technology and the breaking of German naval codes. The Japanese fought the war with an adequate submarine force of 190 submarines and excellent torpedoes, but failed to capitalize on their potential and ignored the strategic importance of antisubmarine warfare. American shipyards poured over 130 new U.S. submarines into the Pacific fleet during the war. The U.S. submarine force went on to sink more than 1300 Japanese merchant ships, 8 aircraft carriers, 1 battleship, and 11 cruisers--a total of 4.75 million tons of ships, accounting for 55 percent of Japan's shipping losses. C Post World War Submarines Both the U.S. and Soviet navies benefited from German submarine technology after World War II. The German U-boats developed late in the war could travel underwater at high speeds and with extended range. This was due to the snorkel, streamlined hull designs, and larger electric batteries. Postwar diesel-electric submarines made the most of these innovations, and underwater maneuverability and speed increased. The beginning of the nuclear age in the 1950s, however, led both sides to embrace reactor power in submarines (and later in surface warships) to increase range and capability even more. The first nuclear-powered submarine, the USS Nautilus, was launched in 1954 and commissioned in the following year. In a trial run conducted in 1955, the Nautilus sailed totally submerged from New London, Connecticut, to San Juan, Puerto Rico, a distance of 2170 km (1350 mi) in 84 hours. Its cruising speed submerged was more than 20 knots, and since the sub was nuclear-powered, it no longer needed to periodically surface for air or for refueling. Early in August 1958 the Nautilus made the first undersea transit of the North Pole, cruising under the polar ice pack from Point Barrow, Alaska, to a point between Spitsbergen, Norway, and Greenland. Superpower submarine fleets grew steadily beginning in the 1950s during the Cold War arms buildup between the United States and the Union of Soviet Socialist Republics. Along with the number of submarines, the size of the subs themselves grew as well. After the fall of the USSR in 1991, the submarine fleets began thinning their ranks and reassessing their strategic and tactical roles. As the 20th century drew to a close, the United States still operated its ballistic missile and attack submarines, but had reduced the orders for newer and costly submarines such as the Seawolf attack subs. A post-Cold War doctrine of operating and fighting in shallow coastal waters emerged, and as a result, the U.S. Navy began revising its training and tactics for future conflicts. Threats of the future may include smaller enemy submarines lurking in shallow waters or in narrow waterways, rather than large subs traveling in deep ocean waters. Some U.S. Navy submarines have been used for scientific missions during the 1990s. In 1995, for example, the U.S. Navy announced the SCICEX (Scientific Ice Expeditions) project, which allowed civilian scientists to conduct missions below the polar ice caps aboard Sturgeon-class attack submarines. The agreement provided for one SCICEX mission a year for five years. Access to this underwater region had been restricted for years due to the harshness of the environment, the distance from support stations, and the danger of other military submarines lurking in the area. The submarines used for these scientific expeditions are specially suited for Arctic missions, and provided a rare opportunity for scientists to explore and map the Arctic Ocean floor, measure ice thickness, and collect water samples. Scientists hoped the missions set the stage for cooperation between the Navy and the scientific community on future expeditions. Contributed By: Ed Offley Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.